We intend in this next project year to extend the current studies on the conversion/crossover problem by imposing additional constraints on our experimental material. In brief, we are utilizing several alleles at the ade6 locus in chromosome VII and studying conversion of various combinations of these alleles. Associated crossing over can be determined in this well-marked chromosome by making use of proximal and distal markers in heterozygous condition. The constraints that we are planning to impose are the incorporation of repair mutants that should affect conversion but not crossing over, and homozygosing the mating type alleles which, in the homozygous condition, are known to reduce the frequency of gene conversion in heteroallelic diploids.